1. Field of the Invention
The invention relates to a solar cell and the method of fabricating the same, and more particularly, to a solar cell overlaid by a multi-atomic-layer structure formed of at least one oxide. In addition, the multi-atomic-layer structure serves as a surface passivation layer, a transparent conductive layer, and further as an anti-reflection layer.
2. Description of the Prior Art
Solar cells are extensively employed because of being capable of converting the accessible energy, emitted from a light source such as the sun, to electricity to operate electronic equipments such as calculators, computers, and heaters.
Referring to FIG. 1, FIG. 1 is a cross section view of the layered stack structure of a conventional silicon solar cell 1.
The conventional silicon solar cell 1 typically includes a p-n junction 13, placed between a p-type substrate 12 and an n-type region 14, located near an illuminated surface (front surface) 11. The term “illuminated surface” herein refers to the surface, exposed to light, of a conventional solar cell whenever it is powered or under operation. Therefore, the term “non-illuminated surface” refers to another surface opposite to the illuminated surface.
Referring to the silicon solar cell 1 in FIG. 1, the basic structure of the p-n junction 13 is formed of an intermediately-doped (about 1015 cm−3) p-type substrate 12 and a heavily-doped (about 1020 cm−3) n-type (n+) region 14, disposed on the substrate 12 and near the illuminated surface 11. The conventional solar cell according to the commercial embodiment typically further includes a surface passivation (or textured) layer 15, formed of an oxide such as silicon dioxide, overlaying the majority of the n-type region 14, an anti-reflection layer 16 overlaying the surface passivation layer 15, an n-type metal contact layer 17 used as an electrode, a p+-type region 18 overlaying a surface of the p-type substrate 12, and a p-type metal contact layer 19 overlaying a surface of the p+-type region 18.
The shallow p-n junction 13 is designed to support the collection of electrons and holes generated on both sides of the p-n junction 13. Each photon of the light penetrates into and is absorbed by the silicon substrate 12, for transferring its energy to an electron in a bound state (covalent bond) and thereby releasing a bound electron to be a free one. This movable electron and the hole (which is also movable) left behind by the former in the covalent bond include a potential element of the current flowing from the solar cell. In order to contribute to the current, the electron and hole cannot recombine but rather are separated by the electric field associated with the p-n junction 13. If the separation occurs, the electron will travel to the n-type metal contact layer 17, and the hole will travel to the p-type metal contact layer 19.
With the development of the silicon solar cell, the structure thereof generating electro-optic effect continues to be investigated such as the multi-junction technique. A variety of the structures related to electro-optic effect inside the silicon solar cell will not be described redundantly here. What is described is only the process of fabricating the surface passivation layer, the anti-reflection layer, and the electrode (which contacts the silicon on the illuminated surface), which is obviously a complicated process.
Accordingly, a scope of the invention is to utilize a multi-atomic-layer structure inside the solar cell. In addition, the multi-atomic-layer structure serves as a surface passivation layer, a transparent conductive layer, and further as an anti-reflection layer. In particular, compared to the prior art, the manufacturing process of the multi-atomic-layer structure is simpler.
Moreover, with the development of the thin film silicon solar cell, the processes, forming each layer inside the thin film silicon solar cell, must lower the possibility of the thermal impact and thermal crack induced on the thin film silicon solar cell to enhance the yield rate.
Accordingly, another scope of the invention relates to a manufacturing process of a solar cell, particularly a thin film solar cell, with the formation of a surface passivation layer, a transparent conductive layer, and further as an anti-reflection layer, in which thermal impact will not occur on the solar cell.